Midget EFI fuel pressure problem

[Morris]

I posted this problem on the Megasquirt board, but it's not getting any action, so I thought I would give you guys a try.

Basically, when I hit the throttle, my fuel pressure drops then stabilizes. Does this sound like a fuel pump or line obstruction?


It's not really a Spridget specific question as my Midget has a homebrew EFI system, but I know most of you guys are very auto savvy beyond the realm Spridgets, so I figured you could probably help me.

 

[BWillis]

Back when I has MS on my 911 I had to use a regulator to keep the pressure constant. It was set to 10 lbs or so less than the rating of the stock fuel pump. When all of the injectors are closed your pump is building up pressure thats higher than what it can sustain during running conditions.

 

[BWillis]

PS,

I would also think that without a regulator your pump is putting out more fuel during idle and making your mixture lean in the higher rpm bands due to less pressure.

Again, this is what I saw in my 911 with MS several years ago.

HTH

 

[RocknTommy]

What FPR are you using now. Adjustable or stock.
Do you have a pic of the setup?

 

[Glen_B]

If you are taking your fuel feed from the stock feed line to the Spridget tank, the line is fairly small diameter to feed an EFI pump. When I do mine, I plan on a larger supply line and use the original line for return. And mentioned above, regulator is important.
That aside, does the O2 sensor show any lean or rich problem associated with the drop/rise of fuel pressure? If not, perhaps the second by second knowledge of exact fuel pressure is a case of too much information irrelevant to normal operation. In other words, fix it by ignoring it.

Glen

 

[Morris]

Ben,

This is a new problem that has only recently surfaced. My pump has not had a problem maintaining constant fuel pressure before. In fact, it must maintain constant fuel pressure for the ECU's calculations to be accurate.

Glen,

I would love to ignore this problem, but it is making the car undrivable. If I step on the throttle, the engine starves for gas so much that it bucks until the fuel pressure comes back up.

Tommy,

I am using a generic adjustable FPR that is widely available on eBay for about $30.00.

I will post pics in another topic.

 

[jlaird]

If this is a new problem it has to be the pump or the regulator dosn't it.

I am assuming nothing else has changed.

 

[BWillis]

I agree.

 

[Morris]

That's what I assumed. I just wanted to get some verification before spending the dough on a pricey new fuel pump.

 

[The_Mite]

Just a thought based on your pictures:
It looks like your fuel pressure regulator has a vacuum port, to regulate the fuel pressure based on manifold vacuum. It will keep your fuel pressure constant in relation to the manifold pressure (or vacuum). With the vacuum port disconnected, your injector will see a large pressure increase when you apply throttle due to the decrease in vacuum in the manifold- perhaps this is causing the lean condition? Maybe if you ported the FPR to the manifold you could cure the problem....

 

[Morris]

Thanks, but I have never ported the FPR to manifold. This problem has only arisen recently.